Process of preparing metals and alloys



preparation of Patented Nov. 10, 1942 PROCESS OF PREPARING METALS ANDALLOYS Eduard Zintl, Darmstadt, and Wilhelm Joseph Morawietz,Bitterfeld, Germany; vested in the Alien Property Custodian N oDrawin'g'. Application December 3, 1940, Serial No. 368,336. In GermanyApril 22, 1939 8 Claims.

The present invention relates to a process of preparing metals andalloys.

If oxides of difllcultly volatile metals are reduced under knownconditions with the aid of silicon or alloys rich in silicon, forinstance ferrosilicon, by heating the mixture under reduced pressure attemperatures between about 1280 C, and about 1350 C. there is obtained amixture of diflicultly volatile metal and silicate which in many casescan be separated in the reaction chamber only with great diiliculties.

Now, we have found a novel process for the metals and alloys which, likethe known, processes, is based on the reduction of difficultly volatileoxides of metals with the aid of silicon but which allows of obtainingin one single operation the metals in a technical-' 1y pure state and ofremoving at thesame time the silicon from the reaction mixture, thusavoiding the formation of silicate residue in the reaction chamber.

The process of the present invention is based on the reduction ofdifl'icultly volatile metal oxides with the aid of silicon attemperatures between 1100 and 2500 C. with volatilization of siliconmonoxide. In order to obtain a metal free from oxygen and silicon thequantity of silicon in the reaction mixture must be such that for 1 atomof oxygen 1 atom of silicon is present. If the mixing proportion is asjust stated and the metal obtained by reduction has a sumciently highboiling point only the siliconmonoxide volatilizes and the metal remainsin a pulverized,'sintered or molten state. For instance, tantalum metalis obtained according to the following equation:

According to another object of the invention it is also possible toobtain metals which are not dimcultly volatile in case the metal may beseparated from the silicon oxide by fractional condensation of thevapors.

Instead of silicon there may be used with the same success for thereduction of the oxide a silicide or a silicon alloy of the metal to beprepared.

It has already been proposed to prepare metals or alloys poor in carbonby silico-thermic reduction of metal oxides by using as reducing agent asilicon alloy in the fused state. But also in this case, as in the knownprocess mentioned above, the formation of a silicate residue in thereaction chamber besides the metal reduced and the resultantdisadvantages already described are unavoidable.

Contrary thereto, according to the process of the present invention, nosilicate residue is formed even if silicon alloys are used as reducingagent but the silicon is volatilized a SiO. The reaction of tantalumoxide and tantalum silicide, for instance, takes place according to thefollowing equation:

Very pure metals are obtained according to the presentprocess if thereaction is carried out in a vessel made of the metal to be prepared.

The process according to the invention may also be applied withadvantage for the direct preparation of alloys. In this case there areheated, instead of one single metal oxide, mixtures or compounds ofseveral metal oxides or mixtures of metal oxides or metal oxidecompounds with metals with corresponding quantities of silicon orsilicides. By application of silicon in excess of the above mentionedproportion oxygen/silicon alloys containing silicon may thus also beobtained.

Since the formation of alloys reduces the vapor pressure of volatilemetals, the losses caused by volatilization are smaller when alloys areformed than when easily volatile metals are prepared in the pure state,

The present process is especially suitable for the preparation of metalsor alloys of the scan- A dium and lanthanum group, the titanium group,

the vanadium group, and the chromium group.

Hitherto the preparation of larger quantities of these elements in thepure state encountered great difliculties. According to the processeshitherto known, for instance, by electrolysis or reduction of oxides orhalides by means of hydrogen, carbon or non-noble metals, there are onlyobtained metals which are more or less contamlnated by oxygemnitrogen orresidues of the reducing agents. By thermic decomposition of compoundspure metals may be obtained, but this process is limited to apreparation on a laboratory scale.

The following examples illustrate the invention, the parts being byweight:

(1) 7.56 parts by weight of pure tantalum pentoxide and 2.79 parts byweight of silicon are intimately mixed' and heated for 5 hours 'in acrucible of tantalum under an absolute pressure of about 10- mm. ofmercury. Oxygen and silicon are entirely volatilized in the form orsilicon monoxide and there remains a lightgray metal powder containing99% of tantalum.

(2) 2.0? parts by weight of finely powdered silicon and 4.00 parts byweight of pure niobium dioxide, NbOz, are intimately mixed, pressed toform pieces and heated for V hour at about 1800 C. under an absolutepressure of mm. of mercury. Thereby the silicon and the oxygen of theoxide volatilize as silicon monoxide and the entire niobium remains as apure, compact and ductile metal. v

It is obvious that our invention is not limited to the foregoingexamples or to the specific details given therein. Thus, for instance,as mentioned above, other diiilcultly volatile metal oxides may bereduced in practically the same manner; the temperatures and the oxygenpressure may be varied in certain limits and the best way for producingcertain metals Irom their oxides is easily determinable by the simpleexperiment,-

the cruxof our invention being the development of SiO for carrying awaythe oxygen the metal oxides under treatment.

What we claim is:

1. The process for diflicultly volatile oxides in the range of thereducing temperature from their oxides by reduction with a siliconcontaining reducing agent by heating them in the ratio corresponding tothe general formula Me=0 +ySi=zMe+ySiQ wherein Me means a metal and a:and 1 are a whole number, under reduced pressure to a temperature atwhich SiO is volatilized.

2. The process for producing metals forming 'dimcultly volatile oxidesin the range of the re-' ducing temperature from their oxides byreduction with a silicon alloy by heating them in the ratiocorresponding to the general formula MeO +uSi=xMe+ySiQ wherein Me meansa metal and a: and 1/ are a whole number, under reduced pressure to'a.temperature at which 810 is volatilized.

3. The process for producing metals forming difilcultly volatile oxidesin the range of the reducing temperature from their oxides byreducproducing metals forming content of tion with ierrosilicium byheating them in the ratio corresponding to the general formula Mee0+y$i=zMe+ySiQ wherein Me means a metal and a: and 11 are a whole number,under reduced pressure to a temperature at which SiO is volatilized.

4. The process for producing metals forming diflicultly volatile oxidesin the range of the reducing temperature from their oxides by reductionwith silicon by heating them in the ratio corresponding to the generalformula MesO ySi=zMe+ySiO number, under reduced pressure to atemperature between 1100 C. and 2500 C.

6. The process for producing metals forming diiiicultly volatile oxidesin the range 01' the reducing temperature from their oxides by reductionwith a silicon containing reducing agent by heating them in the ratiocorresponding to the general formula MeeO +uSi=zMe+ySiQ wherein Me meansa metal and a: and y are a whole number, under a pressure of below 10-mm.- of mercury to a temperature between 1100 C.' and 2500 C.

7. The process for the preparation of tantalum which comprises heatingtantalum pentoxide with silicon in the ratio TazO5:Si=1:5 to reactiontemparature under a pressure of 10 mm. of mercury so that $10 isvolatilized.

8. The process for the preparation of niobium which comprises heatingniobium dioxide with silicon in the ratio NbOaZSi=122 to reactiontemperature under a pressure of 1'() mm. of mercury so that SiO isvolatilized.

EDUARD ZINTL. WILHELM JOSEPH MORAWIETZ.

